Friction plates made from a supporting plate having a friction lining with grooves formed therein for oil guidance for use in clutches, brakes and similar structure have been known for a long time. Usually, the supporting plate is formed of steel and the friction lining formed from a paper-like film of various compositions, mainly consisting of cellulose and synthetic fibers which contain a filler. Before application onto the supporting plate, the friction material is impregnated with a resin-like polymer which is hardened at high temperatures. synchronizer blocker rings with a similar structure, made from a ring core and a friction lining having a paper base applied onto it with grooves for the guidance of oil, are also known.
Conventionally, two methods are used for producing the grooves for the guidance of oil. Either the friction lining is pressed onto the support, that is, onto the supporting plate or ring core, and the grooves are then machined into the friction lining, or, during the pressing process, the grooves are pressed into the friction lining with the aid of an appropriately shaped molding die. In the former process, sharp wiping edges are obtained on the edges of the grooves for wiping the oil. However, these sharp edges are liable to sustain damage during the machining process and also during later operation due to interruption of the homogeneous fiber flow to weaken the structure. The second method has the advantage that the groove rims are considerably more resistant against breaking or flaking, but they do not have the desired wiping effect since they show a slight rounding on the rims. Both methods have the disadvantage that the heat conduction from the oil to the support is impaired by the insulating friction lining.
In order to obtain as high an initial coefficient of friction as possible for the shifting process in a clutch, which frictional coefficient is maintained unchanged until engagement of the clutch, while at the same time the clutch is designed in such a way that the disengaged state of the clutch results in slight entrainment losses; special efforts are necessary in the manufacture of the clutch and in the design of the grooves. In addition, it is very frequently necessary to flush as high a quantity of cooling oil as possible through the grooves during the engaged state of the clutch, while, in the disengaged state, enhanced whirling of the oil should provide additional cooling. It was found that a combination of the desired properties places high demands on the clutch, which cannot always be satisfied by machined or pressed grooves.
A synchronizing blocker ring with a friction lining having a paper base is known from GB Patent No. A-20 06 352, in which a single groove extending through the entire material of the friction lining is designed as a space in the friction lining which is not closed over the entire circumference. However, only a single groove can be formed by having this space between the ends of the friction lining.
In EP Patent No. A-01 28 758 and DE Patent No. B-23 40 464, a friction lining is applied on a supporting plate in a segmented manner, leaving continuous grooves between the segments. The individual production and separate application of several segments of the friction lining is very expensive, last but not least, because of the required precision.